The Dualism of Practical Reason: The Profoundest Problem of ethics

The aim of this article is to discuss and revisit what Sidgwick called the profoundest problem of ethics: the dualism of practical reason. I argue that Crisp’s dual source view provides a good solution for the dualism via the small cost principle showing that we have to balance agent relative and agent neutral reason in a kind of a rational “negotiation” between our egoistic and our altruistic motivations. I suggest, however, that in order to justify his solution it is necessary to go beyond Sidgwick establishing a limit for the acceptance of egoism as a legitimate method of ethics. I propose also that the dualism is not only the profoundest problem of ethics, but also one of the more serious, it is the biggest contemporary ethical puzzle of humankind, and whose practical solution is of paramount importance for the future of life on earth.